Inflatable cooling apparatus for selective organ hypothermia

ABSTRACT

A cooling apparatus having an inflatable balloon near a distal end of a multi-lumen catheter, with a plurality of blood flow passageways formed through the interior of the balloon from a proximal face of the inflated balloon to a distal face of the inflated balloon. Chilled saline solution is introduced through a supply lumen of the catheter to inflate the balloon in a feeding artery of the selected organ; this allows blood to flow through the blood flow passageways of the balloon, from one exterior face of the balloon to another exterior face. The saline solution continues to circulate around the blood flow passageways inside the balloon, to cool the blood, eventually exiting the balloon through a return lumen of the catheter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The current invention relates to selective cooling, or hypothermia, ofan organ, such as the brain, by cooling the blood flowing into theorgan. This cooling can protect the tissue from injury caused by anoxiaor trauma.

2. Background Information

Organs of the human body, such as the brain, kidney, and heart, aremaintained at a constant temperature of approximately 37° C. Cooling oforgans below 35° C. is known to provide cellular protection from anoxicdamage caused by a disruption of blood supply, or by trauma. Cooling canalso reduce swelling associated with these injuries.

Hypothermia is currently utilized in medicine and is sometimes performedto protect the brain from injury. Cooling of the brain is generallyaccomplished through whole body cooling to create a condition of totalbody hypothermia in the range of 20° to 30° C. This cooling isaccomplished by immersing the patient in ice, by using cooling blankets,or by cooling the blood flowing externally through a cardiopulmonarybypass machine.

Total body hypothermia to provide organ protection has a number ofdrawbacks. First, it creates cardiovascular problems, such as cardiacarhythmias, reduced cardiac output, and increased systemic vascularresistance. These side effects can result in organ damage. These sideeffects are believed to be caused reflexively in response to thereduction in core body temperature. Second, total by hypothermia isdifficult to administer. Immersing a patient in ice water clearly hasits associated problems. Placement on cardiopulmonary bypass requiressurgical intervention and specialists to operate the machine, and it isassociated with a number of complications including bleeding and volumeoverload. Third, the time required to reduce the body temperature andthe organ temperature is prolonged. Minimizing the time between injuryand the onset of cooling has been shown to produce better clinicaloutcomes.

Some physicians have immersed the patient's head in ice to provide braincooling. There are also cooling helmets, or head gear, to perform thesame. This approach suffers from the problems of slow cool down and poortemperature control due to the temperature gradient that must beestablished externally to internally. It has also been shown thatcomplications associated with total body cooling, such as arrhythmia anddecreased cardiac output, can also be caused by cooling of the face andhead only.

Selective organ hypothermia has been studied by Schwartz, et. al.Utilizing baboons, blood was circulated and cooled externally from thebody via the femoral artery and returned to the body through the carotidartery. This study showed that the brain could be selectively cooled totemperatures of 20° C. without reducing the temperature of the entirebody. Subsequently, cardiovascular complications associated with totalbody hypothermia did not occur. However, external circulation of theblood for cooling is not a practical approach for the treatment ofhumans. The risks of infection, bleeding, and fluid imbalance are great.Also, at least two arterial vessels must be punctured and cannulated.Further, percutaneous cannulation of the carotid artery is verydifficult and potentially fatal, due to the associated arterial walltrauma. Also, this method could not be used to cool organs such as thekidneys, where the renal arteries cannot be directly cannulatedpercutaneously.

Selective organ hypothermia has also been attempted by perfusing theorgan with a cold solution, such as saline or perflourocarbons. This iscommonly done to protect the heart during heart surgery and is referredto as cardioplegia. This procedure has a number of drawbacks, includinglimited time of administration due to excessive volume accumulation,cost and inconvenience of maintaining the perfusate, and lack ofeffectiveness due to temperature dilution from the blood. Temperaturedilution by the blood is a particular problem in high blood flow organssuch as the brain. For cardioplegia, the blood flow to the heart isminimized, and therefore this effect is minimized.

Intravascular, selective organ hypothermia, created by cooling the bloodflowing into the organ, is the ideal method. First, because only thetarget organ is cooled, complications associated with total bodyhypothermia are avoided. Second, because the blood is cooledintravascularly, or in situ, problems associated with externalcirculation of blood are eliminated. Third, only a single puncture andarterial vessel cannulation is required, and it can be performed at aneasily accessible artery such as the femoral, subclavian, or brachial.Fourth, cold perfusate solutions are not required, thus eliminatingproblems with excessive fluid accumulation. This also eliminates thetime, cost, and handling issues associated with providing andmaintaining cold perfusate solution. Fifth, rapid cooling can beachieved. Sixth, precise temperature control is possible.

The important factor related to catheter development for selective organhypothermia is the small size of the typical feeding artery, and theneed to prevent a significant reduction in blood flow when the catheteris placed in the artery. A significant reduction in blood flow wouldresult in ischemic organ damage. While the diameter of the major vesselsof the body, such as the vena cava and aorta, are as large as 15 to 20mm., the diameter of the feeding artery of an organ is typically only4.0 to 8.0 mm. Thus, a catheter residing in one of these arteries cannotbe much larger than 2.0 to 3.0 mm. in outside diameter. The small sizeof the feeding artery also limits the size and type of heat transferelement that can safely be used.

A catheter based on the circulation of water or saline operates on theprinciple of transferring heat from the blood to raise the temperatureof the water. Therefore, it is essential to use a heat transfer elementthat transfers heat from the blood to the cooling fluid as efficientlyas possible, while restricting the flow of blood as little as possible.So, it would be beneficial to have a heat transfer apparatus that can beinserted percutaneously into an artery of restricted size, that canefficiently transfer heat, and that will not significantly limit theflow rate of blood in the artery during application of cooling.

BRIEF SUMMARY OF THE INVENTION

The present invention is a cooling apparatus comprising a flexiblecatheter which can be inserted through the vascular system of a patientto a feeding artery, with an inflatable balloon heat exchanger near thedistal end of the catheter. The present invention also encompasses amethod for using such a device to perform selective organ cooling. Afterplacement in the selected feeding artery, the heat exchanger balloon isinflated by pressurization with a saline solution, via a supply lumen inthe catheter. The heat exchanger balloon has one or more bloodpassageways passing through it, from a proximal aspect of the balloon toa distal aspect of the balloon. When the heat exchanger balloon isinflated to contact the wall of the artery in which it is placed, eachof the blood passageways comprises a tube having an inlet in one face ofthe heat exchanger balloon and an outlet in another face of the heatexchanger balloon, thereby allowing blood to continue flowing throughthe artery after inflation of the balloon. The blood passageway tubescan be constructed of a material having a relatively high thermalconductivity, such as a thin metallized polymer, such as a film with oneor more metallized surfaces. Alternatively, the blood passageway tubescan be constructed of a metal-loaded polymer film. Further, the entireheat exchanger balloon can be constructed of such a material, in orderto maximize the cooling capacity of the heat exchanger.

After inflation of the heat exchanger balloon, the saline solution,which is chilled by an external chiller, continues circulating throughthe interior of the heat exchanger balloon, around the blood passagewaytubes, and back out of the balloon through a return lumen in thecatheter. This cools the blood passageway tubes, which in turn cool theblood flowing through them. This cooled blood then flows through theselected organ and cools the organ.

The device can also incorporate a lumen for a guidewire, facilitatingthe navigation of the catheter through the vascular system of thepatient.

The novel features of this invention, as well as the invention itself,will be best understood from the attached drawings, taken along with thefollowing description, in which similar reference characters refer tosimilar parts, and in which:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view of the device of the present invention inplace in a common carotid artery of a patient;

FIG. 2 is a perspective view of the device shown in FIG. 1, withadditional details of construction;

FIG. 3 is a transverse section view of the device shown in FIG. 2, alongthe section line 3—3; and

FIG. 4 is a partial longitudinal section view of the device shown inFIG. 2, showing the flow path of the cooling fluid.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, the cooling apparatus 10 of the present inventionincludes a flexible multilumen catheter 12, an inflatable balloon 14,and a plurality of blood flow passageways 16 through the balloon 14. Theballoon 14 is shown in an inflated state, in a selected position in acommon carotid artery CC.

The balloon 14 is attached near a distal end of the flexible catheter12. The catheter 12 can have at least a cooling fluid supply lumen 18and a cooling fluid return lumen 20, with the cooling fluid supply lumen18 preferably being located substantially within the cooling fluidreturn lumen 20. The catheter 12 can also have a guidewire lumen 22, forthe passage of a guidewire 24, as is known in the art.

The balloon 14 can be formed from a flexible material, such as apolymer. The balloon 14 can be constructed to assume a substantiallycylindrical shape when inflated, with a proximal aspect 15 and a distalaspect 17. The balloon 14 can have a plurality of tubular shaped bloodflow passageways 16 formed therethrough, from the proximal aspect 15 tothe distal aspect 17. The tubular walls of the passageways 16 constitutea heat transfer surface, for transferring heat from the blood to thecooling fluid. The flexible material of the tubular passageways 16 canbe, at least in part, a metallized material, such as a film coated witha thin metal layer, either internally, externally, or both, to aid inheat transfer through the passageway walls. Alternatively, the tubularpassageways 16 can be constructed of a metal-loaded polymer film.Further, the remainder of the balloon 14 can be coated with a thinmetallized layer, either internally, externally, or both, or ametal-loaded polymer film. The proximal aspect 15 and the distal aspect17 of the balloon can also constitute a heat transfer surface, fortransferring heat from the blood to the cooling fluid. The guidewirelumen 22 of the catheter 12 can also pass through the balloon 14, fromthe proximal aspect 15 to the distal aspect 17.

As shown in FIG. 2, each tubular passageway 16 has a proximal port 26 ina proximal face 28 on the proximal aspect 15 of the balloon 14, and adistal port 30 in a distal face 32 on the distal aspect 17 of theballoon 14. A cooling fluid supply port 34 near the distal end of thecooling fluid supply lumen 18 supplies chilled saline solution from achiller (not shown) to the interior of the balloon 14, surrounding theblood flow passageways 16. A cooling fluid return port 36 in the coolingfluid return lumen 20 returns the saline solution from the interior ofthe balloon 14 to the chiller. Relative placement of the cooling fluidports 34, 36 can be chosen to establish flow counter to the direction ofblood flow, if desired.

FIG. 3 shows the proximal aspect 15 of the balloon 14 and gives a viewthrough the blood flow passageways 16, illustrating the generalarrangement of the blood flow passageways 16, cooling fluid supply lumen18, cooling fluid return lumen 20, and guidewire lumen 22, within theouter wall 38 of the balloon 14. FIG. 4 is a side elevation view of theapparatus 10, with a partial longitudinal section through the balloonwall 38, showing one possible arrangement of the cooling fluid supplyport 34 and the cooling fluid return port 36 within the balloon 14.

In practice, the balloon 14, in a deflated state, is passed through thevascular system of a patient on the distal end of the catheter 12, overthe guidewire 24. Placement of the guidewire 24 and the balloon 14 canbe monitored fluoroscopically, as is known in the art, by use ofradiopaque markers (not shown) on the guidewire 24 and the balloon 14.When the balloon 14 has been positioned at a desired location in thefeeding artery of a selected organ, such as in the common carotid arteryfeeding the brain, fluid such as saline solution is supplied through thecooling fluid supply lumen 18. This fluid passes trough the coolingfluid supply port 34 into the interior of the balloon 14, surroundingthe tubular passageways 16, to inflate the balloon 14. Although theballoon 14 can be formed to assume a substantially cylindrical shapeupon unconstrained inflation, the balloon 14 will essentially conform tothe shape of the artery within which it is inflated. As the balloon 14inflates, the blood flow passageways 16 open, substantially assuming thetubular shape shown.

When the balloon 14 has been properly inflated, blood continues to flowthrough the feeding artery CC by flowing through the blood flowpassageways 16, as indicated, for example, by the arrows in FIG. 1. Thesize and number of the blood flow passageways 16 are designed to providea desired amount of heat transfer surface, while maintaining a suitableamount of blood flow through the feeding artery CC. Return flow to thechiller can be established, to allow flow of cooling fluid through thecooling fluid return port 36 and the cooling fluid return lumen 20 tothe chiller. This establishes a continuous flow of cooling fluid throughthe interior of the balloon 14, around the blood flow passageways 16.The return flow is regulated to maintain the balloon 14 in its inflatedstate, while circulation of cooling fluid takes place. The salinesolution is cooled in the chiller to maintain a desired cooling fluidtemperature in the interior of the balloon 14, to impart a desiredtemperature drop to the blood flowing through the tubular passageways16. This cooled blood flows through the feeding artery to impart thedesired amount of cooling to the selected organ. Then, cooling fluid canbe evacuated or released from the balloon 14, through the catheter 12,to deflate the balloon 14, and the apparatus 10 can be withdrawn fromthe vascular system of the patient.

While the particular invention as herein shown and disclosed in detailis fully capable of obtaining the objects and providing the advantageshereinbefore stated, it is to be understood that this disclosure ismerely illustrative of the presently preferred embodiments of theinvention and that no limitations are intended other than as describedin the appended claims.

I claim:
 1. A cooling apparatus for selective organ hypothermia,comprising: a flexible catheter; an inflatable balloon attached near adistal end of said catheter; at least one blood flow passageway formedthrough the interior of said balloon, said at least one blood flowpassageway extending from a proximal blood flow port in a proximalexterior face of said balloon to a distal blood flow port in a distalexterior face of said balloon; a cooling fluid supply lumen formed insaid catheter; a cooling fluid supply port in said catheter, connectingsaid cooling fluid supply lumen to the interior of said balloon; acooling fluid return lumen formed in said catheter; and a cooling fluidreturn port in said catheter, connecting the interior of said balloon tosaid cooling fluid return lumen; wherein said at least one blood flowpassageway is formed from a metallized polymer film.
 2. A coolingapparatus as recited in claim 1, wherein said balloon is inflatable to asubstantially cylindrical shape.
 3. A cooling apparatus as recited inclaim 1, wherein said at least one blood flow passageway assumes asubstantially tubular shape upon inflation of said balloon.
 4. A coolingapparatus as recited in claim 1, further comprising a guidewire lumenformed in said catheter.
 5. A cooling apparatus as recited in claim 1,further comprising a plurality of blood flow passageways formed throughthe interior of said balloon, each said blood flow passageway extendingfrom a proximal blood flow port in a proximal exterior face of saidballoon to a distal blood flow port in a distal exterior face of aidballoon.
 6. A cooling apparatus as recited in claim 1, wherein said atleast one blood flow passageway is formed from a polymer film havingmetal layers formed on both interior and exterior surfaces.
 7. A coolingapparatus as recited in claim 1, wherein said at least one blood flowpassageway is formed from a polymer film loaded with metal particles. 8.A cooling apparatus for selective organ hypothermia, comprising: aflexible catheter; an inflatable balloon attached near a distal end ofsaid catheter, said balloon being inflatable to a substantiallycylindrical shape; a plurality of blood flow passageways formed throughthe interior of said balloon, each said blood flow passageway extendingfrom a proximal blood flow port in a proximal exterior face of saidballoon to a distal blood flow port in a distal exterior face of saidballoon, each said blood flow passageway being shaped to assume asubstantially tubular shape upon inflation of said balloon, each saidblood flow passageway being formed of a material having high thermalconductivity; a cooling fluid supply lumen formed in said catheter; acooling fluid supply port in said catheter, connecting said coolingfluid supply lumen to the interior of said balloon; a cooling fluidreturn lumen formed in said catheter; and a cooling fluid return port insaid catheter, connecting the interior of said balloon to said coolingfluid return lumen; wherein each said blood flow passageway is formedfrom a metallized polymer film.
 9. A cooling apparatus as recited inclaim 8, wherein each said blood flow passageway is formed from apolymer film having metal layers formed on both interior and exteriorsurfaces.
 10. A cooling apparatus as recited in claim 8, furthercomprising a guidewire lumen formed in said catheter.
 11. A coolingapparatus as recited in claim 8, wherein each said blood flow passagewayis formed from a polymer film loaded with metal particles.